Conventionally, for a ring of a thrust needle (needle) roller bearing or a ring of a drawn cup radial needle roller bearing, a low-carbon SPCC (JIS: a cold rolled steel plate) product, an SCM415 product (JIS: a steel product of chromium molybdenum steel) and the like carburized for a short period of time and a hardness-requiring portion of the surface layer is hardened have been used. Also, products of mid-to high-carbon steel have been manufactured, such as an SK5 product (JIS: a steel product of carbon tool steel) subjected to through quenching by whole heating. With all of these, carburizing or a batch type furnace have been used in heat treatment.
On the other hand, in some applications quenching of a thin product by high-frequency heating has also been performed. Conventionally, as to quenching of a thin product or an uneven-thickness component by high-frequency heating, there are techniques that can be found in the following Patent Documents 1-4. All of these, however, employ air or gas for cooling in quenching so as to control the cooling rate for suppressing distortion, or to eliminate difference in quenching speed between a thick portion and a thin portion for suppressing deformation.
As to a tubular member, while there is a technique of providing constraint in quenching can be found (for example, Patent Document 5), it employs a solution in quenching. Hence, there has been no technique employing a mold for constraining and also as a quenching medium.
Patent Document 1: Japanese Patent Laying-Open No. 6-179920
Patent Document 2: Japanese Patent Laying-Open No. 9-302416
Patent Document 3: Japanese Patent Laying-Open No. 2001-214213
Patent Document 4: Japanese Patent Laying-Open No. 2003-55713
Patent Document 5: Japanese Patent Laying-Open No. 7-216456